The chairman of the Nuclear Regulatory Commission says it may seem unlikely that a blizzard three decades ago caused cracks that were only recently discovered in the concrete shield around the Davis Besse nuclear plant. But Gregory Jaczko stands behind those controversial findings.

First Energy operates the plant east of Toledo and determined earlier this year that the blizzard of 1978 drove water into the thick concrete and caused cracking when it froze.

This week the NRC accepted that analysis and that the facility is safe. Chairman Jaczko.

“It certainly I think is … a cause that in the end may always be controversial or challenged as to what the actual cause was. But … more importantly right now are the symptoms and making sure that those symptoms don’t have any impact on safety. And right now we don’t see any, but we’ll continue to monitor that going forward.”

Critics challenge that explanation, and say it’s one reason Davis Besse’s operating license should not be extended for another 20 years.

First-Energy spokeswoman Jennifer Young says the company is fixing the problem beyond what’s required.

“We’re taking some action this summer to apply a sealing coating, basically painting the building to ensure that we don’t have any water intrusion in the future. At the time that building was constructed, that coating was not spec’d into it. It was not part of code requirements then, and it remains not part of code requirements to have this kind of coating.